JP2009528579A - Audio decoding technology for mid / side stereo - Google Patents

Abstract

This disclosure describes a decoding technique for audio information encoded with mid / side (MS) stereo encoding. The technique involves a number of audio decoding tasks that are performed in an unconventional order. By rearranging the order of the decoding tasks, various effects can be obtained. In one embodiment, a method for decoding MS stereo audio information includes decoding a first channel of audio information and calculating an inverse modified discrete cosine transform (IMDCT) for the first channel in preference to generating MS stereo information. Decoding the second channel of audio information, calculating IMDCT for the second channel in preference to generating MS stereo information, and MS stereo information using each IMDCT for the first and second channels Generating.

Description

  The present disclosure relates to audio coding techniques, and more particularly to decoding techniques for audio information encoded with mid-side (MS) stereo encoding techniques.

  Audio coding is used in many applications and environments such as satellite radio, digital radio, Internet streaming (web radio), digital music players, and various mobile multimedia applications. There are many audio coding standards, such as those from the Motion Pictures Expert Group (MPEG), Windows Media Audio (WMA), and Dolby Laboratories. There is a standard by the company. Many audio coding standards, including the MP3 standard and the successor to the MP3 standard, such as advanced audio coding (AAC) used in “iPod” devices sold by Apple Computer, Inc. And continues to appear. In general, audio coding standards aim to achieve low bit rates and high-quality audio coding using compression techniques. Some audio coding is “lossless”, that is, coding does not degrade the audio signal, while other audio coding leads to some loss for the purpose of more compression than expected.

  In many applications, audio coding is used in conjunction with video coding to provide multimedia content for applications such as video telephony (VT) or streaming video. MPEG video coding standards, for example, often use audio coding and video coding. MPEG standards currently include MPEG-1, MPEG-2 and MPEG-4, but other standards will likely emerge. Another typical video standard is the International Telecommunications Union (ITU) H.264 standard. H.263 standard, ITU H.264 H.264 standard, Quick Time (TM) technology developed by Apple Computer, Video for Windows (TM) developed by Microsoft, Indeo (TM) developed by Intel, Real Video (TM by Real Network) ), Cinepack (TM) developed by Super Mac. Some audio and video standards are open source, while others remain proprietary. Many other audio and video coding standards will emerge and evolve one after another.

  Stereo coding refers to audio coding that uses two different coding channels. Stereo coding can improve the quality of perceived speech that humans perceive from decoded audio signals because humans have two ears and they recognize speech in terms of directionality. One relatively intuitive method of encoding stereo sound information is to use left and right channels to encode the left and right signals, respectively. However, for complex audio such as musical recordings, the left and right encoding channels are not particularly effective because the left and right microphones can detect the same sound with different delay times. As a result, mid-side (MS) stereo was developed to improve the quality of stereo sound.

  In MS stereo, two different signals are used to encode the location of the audio source and the echo environment of the stereo image, respectively. Basically, MS stereo is encoded via a center signal and a side signal. Following decoding, the left channel is generally the sum of the two encoded channels and the right channel is generally the difference between the two encoded channels. By using the center stereo component and the horizontal stereo component, stereo in the left and right channels can be achieved to achieve higher quality stereo coding and to achieve better compression levels for a given sound quality level. Redundancy can be exploited.

[Overview]
The present disclosure describes a decoding technique for audio information encoded according to mid / side (MS) stereo encoding. The technique involves several audio decoding tasks that are performed in a non-conventional order. By rearranging the order of the decoding tasks, various effects can be obtained. For example, the latency in the decoding process is such that the computational task for the inverse modified discrete cosine transform (IMDCT) for the first channel is parallel to the pre / decoding task for the second channel. Can be removed or reduced by approving it to be executed. Specifically, when used in conjunction with direct memory exchange (DME) technology, the technology is used in the decoding of the other channel that is performed in parallel with the IMDCT calculation for one channel. Allows the retrieval of memory for loading a decoding table (eg, a Huffman table). In this way, the technology will provide computational advantages and accelerate the audio decoding process.

  In one embodiment, the present disclosure provides an apparatus that includes a memory that stores encoded audio information and a decoder unit that decodes the information. The decoder unit decodes the first channel of audio information, calculates IMDCT for the first channel prior to generation of MS stereo information, decodes the second channel of audio information, and prior to generation of MS stereo information. Calculate the IMDCT for the second channel. MS stereo information is then generated using IMDCT for the first and second channels.

  In another embodiment, this disclosure provides a method for decoding MS stereo audio information. The method decodes a first channel of audio information, calculates an IMDCT for the first channel prior to generation of MS stereo information, decodes a second channel of audio information, and precedes generation of MS stereo information. Calculating IMDCT for the second channel and generating MS stereo information using the IMDCT for the first and second channels. In order to take advantage of the technique, a memory fetch to load the decoding table for the second channel can be performed during the IMDCT calculation for the first channel.

  The above and other techniques described herein may be implemented in hardware, software, firmware, or any combination thereof. If executed in software, the software may be executed in a digital signal processor (DSP) or other type of processor. Software that implements the technique is initially stored in a computer readable medium, loaded and executed in the DSP for effective audio decoding of audio information encoded according to MS stereo. It may be.

  As a result, the present disclosure decodes the first channel of audio information, calculates the IMDCT for the first channel prior to generation of the MS stereo information, and executes the second of the audio information when executed on an apparatus that supports MS stereo. A computer comprising executable instructions for decoding the channel, calculating the IMDCT for the second channel prior to generating the MS stereo information, and generating the MS stereo information using the IMDCT for the first and second channels A readable medium is also considered.

  In yet another embodiment, the present disclosure provides that a decoder unit decodes a first channel of audio information, calculates a transform for the first channel prior to generating MS stereo information, and decodes a second channel of audio information. A decoder unit for an audio decoding device is provided that calculates a transform for a second channel prior to generating MS stereo information and generates MS stereo information using the transform for the first and second channels .

  Additional details regarding various embodiments are set forth in the accompanying drawings and the description below. Other features, intentions, and advantages will be apparent from the description and drawings, and from the claims.

[Detailed description]
The present disclosure describes a decoding technique for audio information encoded by mid / side (MS) stereo encoding. Two different signals in MS stereo are used to encode the location of the audio source and the echo environment of the stereo image, respectively. Basically, MS stereo is encoded from the center signal and the side signal. Following MS stereo decoding, the left channel is generally the sum for the first and second encoded channels, and the right channel is generally the difference between the first and second encoded channels. The left and right channels can be interchanged.

  Conventional MS stereo decoding requires channel 1 dequantization after channel 1 decoding. Channel 2 is then decoded and then channel 2 is dequantized. Thereafter, stereo information for the left and right channels is calculated from the decoded channel 1 and channel 2. For example, the left channel MS stereo information may include channel 1 + channel 2, and the right channel MS stereo information may include channel 1-channel 2. An inverse modified discrete cosine transform (IMDCT) is then performed on the left channel stereo information, windowing is performed, and an audio sample is rendered on the left channel. Similarly, IMDCT is performed on the right channel stereo information, windowing is performed, and audio samples are provided on the right channel. Thus, conventional MS stereo decoding is generally a sequential process in which IMDCT is performed following generation of MS stereo information.

  The techniques described in this disclosure may include steps similar to conventional MS stereo decoding, but perform the steps in an unusual order. Specifically, according to the present disclosure, IMDCT is performed for channel 1 and channel 2 prior to the generation of MS stereo information for the left and right channels. By rearranging the order of the decoding tasks, various effects can be obtained. For example, latency in the decoding process is eliminated or reduced by allowing the computational task for IMDCT for the first channel to be performed in parallel with the pre / decoding task for the second channel. It is possible. In particular, when a direct memory exchange (DME) technique is used in a digital signal processor (DSP), the technique is such that the decoding table memory fetch for one channel is performed in parallel with the IMDCT calculation for the other channel. Make it possible. In this way, the techniques described herein may provide computational benefits and accelerate the audio decoding process.

  DME technology generally relates to fetching digital signal processed (DSP) memory that is performed in parallel with being processed by the DSP during clock cycles within the DSP. Any other type of memory or processing technology may be used, especially any technology that supports the ability to load memory into an on-chip processor storage location in parallel while the processor performs a computational task May also be used.

  FIG. 1 is a block diagram of an audio decoding device 10 that can implement the techniques of this disclosure. As shown, the apparatus 10 includes a memory 12 and an MS stereo decoding unit 14. The memory 12 may store audio information encoded according to MS stereo. Audio information may have been received over a communication channel such as real-time audio or stored in memory 12 for an extended period of time. In order to improve the decoding process of audio information, decoding unit 14 performs one or more of the techniques of this disclosure. In particular, the decoding unit 14 decodes the first channel of audio information, calculates the IMDCT for the first channel prior to generating the MS stereo information, decodes the second channel of audio information, and generates the MS stereo information. Prior to, IMDCT for the second channel is calculated and MS stereo information is generated using each IMDCT for the first and second channels. Thereafter, the MS stereo information may be used to generate signals that drive the left and right speakers 16A and 16B. In particular, the drive circuit 15 may receive MS stereo information from the MS stereo decoding unit 14 and generate drive voltages for the speakers 16A and 16B based on the MS stereo information. The drive circuit 15 includes one or more digital-to-analog converter (DAC), power amplifiers and other analog signal conditioning components.

  The so-called “bottleneck” or failure in MS decoding requires both conventional MS decoding to decode the encoded channel and that MS stereo information is generated prior to performing IMDCT. This can happen because of the fact that However, according to the present disclosure, the IMDCT for each encoded channel (channels 1 and 2) may be performed prior to the generation of MS stereo information for the left and right channels. The linearity observed for IMDCT allows this change.

  Furthermore, the benefits can be gained by utilizing parallel processing by rearranging the steps of the decoding process. For example, latency in the decoding process may be eliminated or reduced by allowing decoding unit 14 to perform IMDCT for the first channel in parallel with the pre / decoding task for the second channel. In particular, when used in conjunction with DME technology or similar technology that supports memory retrieval during computation, the technology allows the decoding unit 14 to perform memory retrieval from the memory 12 in parallel with the IMDCT computation. Can do. Memory fetching can load a decoding table (eg, a Huffman table) for the purpose of being used in decoding one channel. At the same time, an IMDCT calculation can be performed for the other channel. In this way, the decoding unit 14 can have a computational effect and the audio decoding process can be accelerated.

  Device 10 may include any of a wide variety of devices that may include audio decoding capabilities. Examples include digital music players such as iPods, digital television, digital direct broadcast systems, wireless communication devices, personal digital assistants (PDAs), laptop computers, desktop computers, digital cameras, digital recording devices , Cellular or satellite radio telephones, direct two-way communication devices (sometimes called "walkie talkies"), and the like.

  FIG. 2 is a flow diagram illustrating a decoding process that may be performed by decoding unit 14. As shown, decoding unit 14 decodes the first channel of audio information (21) and then calculates the IMDCT for the first channel prior to generating MS stereo information (25) (22). The decoding unit 14 then decodes the second channel of audio information (23) and calculates the IMDCT for the second channel (24) prior to the generation of MS stereo information (25).

The IMDCT calculation for the first and second channels may substantially follow Equation 1 and Equation 2 below.

Where L_channel_time_output 'means IMDCT for channel 1
R_channel_time_output 'means IMDCT for channel 2
L and R mean the left and right channel spectral coefficients respectively,
N means the audio frame length in the decoder unit 14,
K means frequency index of spectrum coefficient,
n means the time index, and n0 is a constant.

  However, in other embodiments, the decoder unit 14 may use other types of transforms rather than IMDCT.

  As shown in FIG. 2, the decoding unit generates MS stereo information using IMDCT for the first and second channels (25). The MS stereo information includes left and right channel information that can be used to generate audio samples, which can be used in turn to define drive signals for the left and right speakers 16A and 16B. Furthermore, the left channel information may be an additive combination for IMDCT from channels 1 and 2, while the right channel information may be a subtractive combination for IMDCT for channels 1 and 2. However, the right and left channels are interchangeable, and the left channel may be defined as an additive combination for IMDCT and the right channel is defined as a subtractive combination of IMDCT. It should be noted that the generation of MS stereo information occurs after the IMDCT calculation.

  In many cases, decoding unit 14 may also perform dequantization for the first and second channels. Specifically, decoding unit 14 may dequantize the first channel of audio information prior to the calculation of IMDCT for the first channel, and audio information prior to the calculation of IMDCT for the second channel. Quantization may be performed for the second channel.

  In some cases, decoding of the first and second channels may include Huffman decoding or other similar decoding using a look-up table. In such cases, a look-up table (eg, a Huffman table) may need to be loaded from memory 12 to decoding unit 14 for each encoded channel, and again for successive audio frames. Sometimes loaded. Unfortunately, the Huffman table can be relatively large, especially when the decoding unit 14 is provided as a DSP that does not include large on-chip memory. In accordance with the present disclosure, the Huffman table for the first channel may be loaded from the memory 12 to the decoding unit 14 prior to decoding the first channel, and during the IMDCT calculation for the second channel. A Huffman table for two channels may be loaded from the memory 12 into the decoding unit 14. Decoding unit 14 may include a DSP with local on-chip memory that is large enough to store a Huffman table, but insufficient to store several such tables.

  Memory loading performed in parallel while performing the IMDCT calculation is particularly effective when the decoding unit 14 includes a DSP that supports direct memory exchanges (DMEs). In this case, simultaneously with performing the IMDCT calculation for the current channel, the DSP can perform a memory fetch in order to load the next Huffman table required for decoding the next channel. In addition, successive parallel computations and memory fetches can be performed on successive audio frames. In particular, if the audio information is divided into a number of audio frames in the audio sequence, the decoding unit 14 will perform a Huffman for the first channel of the first audio frame prior to decoding the first channel of the first audio frame. Loading table, loading IMFCT for second channel of first audio frame during calculation of IMDCT for second channel of first audio frame, and calculating IMDCT for second channel of first audio frame May load the Huffman table for the first channel of the second audio frame. In this way, simultaneous computation and memory fetching can be performed with the decoding of each channel in successive audio frames.

  FIG. 3 is yet another flow diagram illustrating aspects of an audio decoding process in accordance with the present disclosure. As shown in FIG. 3, decoding unit 14 loads a lookup table from memory 12 for channel 1, for example, via direct memory access (DMA) (31). Thereafter, the decoding of channel 1 is started (32) using, for example, a loaded lookup table. Thereafter, simultaneously with loading another look-up table from memory 12 for channel 2 (34), eg, via a direct memory exchange (DME), decoding unit 14 calculates an IMDCT for channel 1 (33). ). The decoding unit 14 can then decode channel 2 (35) and calculate the IMDCT for channel 2 (36).

  The decoding unit then generates MS stereo information for channels 1 and 2 using the IMDCT for each channel (35). The MS stereo information includes left and right channel information that can be used to generate audio samples, which can be used in turn to define drive signals for the left and right speakers 16A and 16B. As described above with respect to FIG. 2, decoding unit 14 may also perform dequantization for channels 1 and 2, for example, prior to respective IMDCT calculations for each channel. In either case, the generation of MS stereo information (37) occurs after the IMDCT calculation (33 and 36). Decoding unit 14 may then provide the possibility to perform windowing and audio samples for the left and right channels (38). Audio samples may be used by drive circuit 15 to define the number of volts required to drive speakers 16A and 16B for stereo output.

  Again, in accordance with this disclosure, the simultaneous calculation of the IMDCT involving the DME loading the next lookup table to be used in decoding is performed for channels 1 and 2 of successive audio frames in the audio sequence. May happen repeatedly. FIG. 4 illustrates the technique that is advantageous in situations where Huffman decoding is performed on a series of audio frames.

  As shown in FIG. 4, decoding unit 14 loads a Huffman table from memory 12 for channel 1 of the first frame in the audio sequence, eg, via DMA (41). Decoding unit 14 then decodes channel 1 using the loaded Huffman table (42). The decoding unit 14 then loads another Huffman table from the memory 12 for channel 2 of the first frame, for example via DME (43) and at the same time calculates the IMDCT for channel 1 of the first frame ( 44). Decoding unit 14 may then decode channel 2 of the first frame using the Huffman table loaded during the IMDCT calculation for channel 1 of the first frame (45).

  The decoding unit then loads (46) another Huffman table from memory 12 for channel 1 of the second frame in the audio sequence, eg via DME, at the same time for channel 2 of the first frame. IMDCT is calculated (47). Decoding unit 14 may then decode channel 1 of the second frame using the Huffman table loaded during the IMDCT calculation for channel 2 of the first frame (48).

  The decoding unit 14 then loads (49) another Huffman table from the memory 12 for channel 2 of the second frame in the audio sequence, for example via DME, at the same time as channel 1 of the second frame. IMDCT for is calculated (50). Decoding unit 14 may then decode channel 2 of the second frame using the Huffman table loaded during the IMDCT calculation for channel 1 of the second frame (51).

  The decoding unit 14 then loads (49) another Huffman table from the memory 12 for channel 1 of the third frame in the audio sequence, for example via DME, at the same time as channel 2 of the second frame. Calculate IMDCT for (53). This process can continue for any number of MS encoded audio frames in the audio sequence. Along with each subsequent IMDCT calculation, a concurrent memory fetch and next required Huffman table load can be performed to reduce latency, accelerating the decoding process. Is possible.

  A number of embodiments have been described so far. However, various modifications can be made to the techniques described herein. For example, MS stereo may consist of two channels, or may reference for two channels for a multi / channel system such as a multi / channel surround system. In addition, other types of transforms rather than IMDCT may be used for MS stereo decoding. Also, although the present disclosure has referenced Huffman tables for Huffman coding, other types of coding can be used according to the present disclosure. Huffman coding is an effective example because it results in lossless encoding and decoding of audio information. Other coding techniques may also benefit from the teachings of this disclosure. In particular, lookup coding techniques that require loading from memory for each channel of successive audio frames may benefit from the teachings of this disclosure.

  The techniques described herein may be implemented in hardware, software, firmware, or any combination thereof. When implemented in software, the techniques include computer code that includes program code that performs one or more of the audio decoding techniques described herein when executed in an apparatus that encodes a video sequence. May be directed to various media. In this case, the computer-readable medium is, for example, a synchronous dynamic random access memory (SDRAM), a read-only memory (ROM), a non-volatile memory (NVRAM), or an electrically erasable and programmable read-only memory (EEPROM). May include random access memory (RAM), such as flash memory.

  The program code may be stored in memory in the form of computer readable instructions. In that case, a processor such as a DSP may execute instructions stored in memory for the purpose of performing one or more audio decoding techniques. The technique may be performed by a DSP that employs various hardware components to accelerate the coding process. On the other hand, the units described here may be microprocessors, one or more application specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs), or some other hardware. / May be provided as a software combination.

  These and other embodiments are within the scope of the following claims.

FIG. 6 is a block diagram of an example audio decoding device that can implement the techniques of this disclosure. FIG. 2 is a flow diagram illustrating a technique performed by the audio decoding device of FIG. 1 or other similar devices. FIG. 2 is a flow diagram illustrating a technique performed by the audio decoding device of FIG. 1 or other similar devices. FIG. 2 is a flow diagram illustrating a technique performed by the audio decoding device of FIG. 1 or other similar devices.

Claims (26)

An apparatus comprising a memory for storing encoded audio information, and a decoder unit for decoding the encoded information,
The decoder unit decodes the first channel of audio information;
Calculating an inverse modified discrete cosine transform (IMDCT) for the first channel prior to generation of mid / side (MS) stereo information;
Decoding the second channel of audio information;
Calculate the IMDCT for the second channel prior to generating the MS stereo information; and
An apparatus operable to generate MS stereo information using each IMDCT for the first and second channels. The decoder unit is
Operable to perform dequantization for the first channel of audio information prior to calculation of IMDCT for the first channel, and second channel of audio information prior to calculation of IMDCT for the second channel The apparatus of claim 1, wherein the apparatus is operable to perform dequantization on.   In addition, left and right stereo speakers are included, the MS stereo information comprises left and right channel information, and the decoder unit can perform windowing on the left and right channel information, and the left and right stereo speakers The apparatus of claim 1, wherein the apparatus provides an audio specimen.   The apparatus of claim 1, wherein decoding the first channel includes Huffman decoding the first channel, and decoding the second channel includes Huffman decoding the second channel.   The decoding unit is operable to load a Huffman table for the first channel prior to decoding the first channel, and for the second channel while calculating the IMDCT for the first channel The apparatus of claim 4, wherein the apparatus is operable to load a Huffman table.   The apparatus of claim 1, wherein the decoding unit is operable to decode the first and second channels for a plurality of audio frames in the audio sequence. The decoding unit is operable to perform Huffman decoding,
Note that the decoding unit loads the Huffman table for the first channel of the first audio frame prior to decoding the first channel of the first audio frame;
Loading the Huffman table for the second channel of the first audio frame while calculating the IMDCT for the first channel of the first audio frame and second while calculating the IMDCT for the second channel of the first audio frame The apparatus of claim 6, wherein the apparatus is operable to load a Huffman table for a first channel of an audio frame.   The apparatus of claim 1, wherein the decoding unit includes a digital signal processor (DSP) that supports direct memory exchanges (DMEs).   The device includes at least one of a digital music player, a wireless communication device, a personal digital assistant (PDA), a laptop computer, a desktop computer, a digital camera, a digital video recording device, a wireless telephone, and a direct two-way communication device. The apparatus of claim 1, comprising: A method for decoding mid / side (MS) stereo audio information, comprising:
Decoding the first channel of audio information;
Calculating an inverse modified discrete cosine transform (IMDCT) for the first channel prior to generating the MS stereo information;
Decoding the second channel in the audio information;
Calculate the IMDCT for the second channel prior to generating the MS stereo information; and
Generating MS stereo information using each IMDCT for the first and second channels;
Including methods. In addition, dequantization for the first channel of audio information is performed prior to calculation of IMDCT for the first channel, and dequantization for the second channel of audio information is performed prior to calculation of IMDCT for the second channel. The method of claim 10, comprising performing an initialization.   11. The method of claim 10, wherein the MS stereo information includes left and right channel information, further performing windowing on the left and right channel information, and for left and right stereo speakers The method of claim 10, comprising providing an audio specimen.   The method of claim 10, wherein decoding the first channel includes Huffman decoding the first channel and decoding the second channel includes Huffman decoding the second channel.   In addition, loading the Huffman table for the first channel prior to decoding the first channel, and loading the Huffman table for the second channel while calculating the IMDCT for the first channel. 14. The method of claim 13, comprising.   The method of claim 10, further comprising decoding first and second channels of a plurality of audio frames in the audio sequence. 16. The method of claim 15, wherein decoding the first and second channels comprises Huffman decoding the first and second channels,
A decoding unit loads a Huffman table for the first channel of the first audio frame prior to decoding the first channel;
Loading the Huffman table for the second channel of the first audio frame while calculating the IMDCT for the first channel of the first audio frame and second while calculating the IMDCT for the second channel of the first audio frame 16. The method of claim 15, comprising loading a Huffman table for the first channel of an audio frame. A computer readable medium containing instructions executable on a device that supports mid / side (MS) stereo,
Decoding the first channel of audio information;
Calculating an inverse modified discrete cosine transform (IMDCT) for the first channel prior to generating the MS stereo information;
Decoding the second channel of audio information;
Calculate the IMDCT for the second channel prior to generating the MS stereo information; and
A computer readable medium containing executable instructions for generating MS stereo information using each IMDCT for the first and second channels. In addition, performing dequantization on the first channel of audio information prior to the calculation of IMDCT for the first channel; and
18. The computer readable medium of claim 17, comprising instructions for performing dequantization on a second channel of audio information prior to calculating an IMDCT for the second channel.   18. The computer of claim 17, wherein the MS stereo information includes left and right channel information and the instructions perform windowing on the left and right channel information and provide audio samples for the left and right stereo speakers. A readable medium.   The computer-readable medium of claim 17, wherein the instructions decode the first channel using Huffman decoding and the instructions decode the second channel using Huffman decoding. 23. The instructions load the Huffman table for the first channel prior to decoding the first channel and load the Huffman table for the second channel during the IMDCT calculation for the first channel. Computer readable media.   The computer-readable medium of claim 17, wherein the instructions decode first and second channels of a plurality of audio frames in an audio sequence.   The instruction uses Huffman decoding, and the instruction loads a Huffman table for the first channel of the first audio frame prior to decoding the first channel of the first audio frame; Loading the Huffman table for the second channel of the first audio frame while calculating the IMDCT for the first channel of the frame, and the second audio frame while calculating the IMDCT for the second channel of the first audio frame 23. The computer readable medium of claim 22, loading a Huffman table for a first channel of the first. A decoder unit for an audio decoding device,
The decoder unit is
Decoding the first channel of audio information;
Calculate the transformation for the first channel prior to the generation of mid / side (MS) stereo information;
Decoding the second channel of audio information;
Calculating a transform for the second channel prior to generating the MS stereo information; and
Operable to generate MS stereo information using transforms for the first and second channels;
Decoder unit for audio decoding equipment.   The decoder unit of claim 24, wherein the transform for the first and second channels comprises an inverse modified discrete cosine transform (IMDCT).   The decoder unit is operable to load a table for decoding the first channel prior to decoding the first channel, and for the second channel while calculating the transform for the first channel 25. A decoder unit according to claim 24, operable to load a table.

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